More than 40,000 spectators watched as a cascade of white balloons was released to open London's Olympic stadium on Saturday, exactly 2,012 hours before the Games begin.

Capping off an evening of music, comedy and fun sports events, Paralympic gold medal-winning archer Danielle Brown shot arrows at spinning targets to select the name of a youngster in the audience to open the east London stadium.

A dazed-looking Niamh Clarke-Willis, 9, joined Sebastian Coe, the chairman of Games organisers LOCOG, in pressing a large button to release the balloons into the chilly night sky over the stadium.

The 80,000-capacity venue hosts the Olympic opening ceremony on July 27.

Coe, himself an Olympic gold medallist, said it felt "barely believable" to be opening the stadium, adding: "I'm just so grateful to everybody who's come here tonight to help us celebrate this moment in history."

"I walked around anonymously last night and I was just listening to the excitement of the people who were walking in, it was a bit like watching my kids on the first day they woke up to find snow in the back garden."

"The seven years have just flown by," he said. "Tonight is only the start of the story. We want thousands of young people to be inspired to take up sport. We hope that for a few of them it will be the start of their journey."

Saturday's event, named "2012 Hours to Go: An Evening of Athletics and Entertainment", allowed organisers to test the Olympic Park's airport-style security checks.

It was also a major test of London's transport system ahead of the Games as the Underground train network's Jubilee line, which serves the stadium, was further crammed with football fans leaving the FA Cup final in north London.

The crowds at the stadium watched as Olympic rowing champion Steve Redgrave and Downton Abbey actor Hugh Bonneville joined other celebrities and sport stars in a series of fun contests to test out the running track.

Former Spice Girl Melanie C and comedian Jack Whitehall performed, while the Military Wives, a group of British soldiers' wives whose charity single topped the charts last Christmas, led a rendition of the national anthem.

Earlier, students had tested out the stadium as part of the British Universities and Colleges Sport championships.

The stadium, at the centre of the Olympic Park in a formerly rundown part of east London, will go into lockdown from May 12 as organisers put the final touches on the facility.

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